The following includes information that may be useful in understanding various aspects and embodiments of the present disclosure. It is not an admission that any of the information provided herein is prior art, or relevant, to the presently described or claimed inventions, or that any publication or document that is specifically or implicitly referenced is prior art.
The therapeutic potential of induced pluripotent stem cells (iPSCs) has spurred efforts to develop reprogramming methods that sidestep the need to genetically modify somatic cells to effect reprogramming to the pluripotent state. The first “non-integrating” approaches to achieve success in this regard—protein transduction, plasmid transfection and the use of adenoviral vectors—were limited in application due to the low efficiencies of iPSC conversion attained. More recently, techniques employing episomal DNA, Sendai virus, and synthetic messenger RNA (mRNA) have been shown to generate “footprint-free” iPSCs with efficiencies comparable to or surpassing those attained using integrating viral vectors. RNA transfection is in principle the most attractive of these methods as it affords precise control over the reprogramming factor (RF) expression time course, while completely obviating any requirement for “clean up” of the reprogrammed cells to purge residual traces of the vector. Current protocols for mRNA-based reprogramming are relatively labor-intensive, however, owing to the need to retransfect daily for the ˜2 weeks required for the induction of pluripotency in human cells. These procedures also rely on the use of feeder cells, adding complexity and technical variability to the process while introducing a potential source of contamination with non-human-derived (“xeno”) biological material.
A major difficulty of producing induced pluripotent stem cells (iPSCs) has been the low efficiency of reprogramming differentiated cells into pluripotent cells. Previously, it has been reported that 5% of mouse embryonic fibroblasts (MEFs) were reprogrammed into iPSCs when they were transduced with a fusion gene composed of Oct4 and the transactivation domain of MyoD (called M3O), along with Sox2, Klf4 and c-Myc (SKM). In addition, M3O facilitated chromatin remodeling of pluripotency genes in the majority of transduced MEFs, including cells that did not become iPSCs. These observations suggested the possibility that more than 5% of cells had acquired the ability to become iPSCs given more favorable culture conditions.